The present invention relates to a servo pattern forming method for a floppy disk and more particularly to a method of writing servo patterns to a floppy disk by the use of a magnetic head having a magnetic head gap wider than the track pitch of the floppy disk. This method can perform the writing without giving rise to any write overlap portion of the written servo patterns.
Generally, a servo pattern written to a disk-shaped recording medium comprises servo information and burst and is formed wider than the data track width.
FIG. 7 is an enlarged plan view showing an example of configuration of such a servo pattern.
As shown in FIG. 7, a servo pattern 71 comprises servo information 72 and burst 73 and it is wider than the width of a data track 74. The servo information is written in such a manner that a center line (information center) of each information area coincides with a center line (track center) 75 of each data track 74. The burst 73 is written in such a manner that the outer and inner edges of each information area are respectively in contact with the center lines (track centers) 75 of adjacent data tracks 74.
For writing a servo pattern to a floppy disk as a disk-shaped recording medium, there usually is employed a magnetic head for read/write (R/W) which is disposed on the floppy disk drive side. The R/W magnetic head has a head gap equal to the data track width (data width) of the floppy disk. Therefore, in writing servo patterns with use of the R/W magnetic head, first a servo pattern is written to one-side portion of a single track, then the R/W magnetic head is moved a predetermined distance, that is, a half track pitch for example, in a direction perpendicular to the track (radial direction of the floppy disk), and then a servo pattern is written (overlap write) in the same position as the previously written position. In this way servo patterns are written over a predetermined width.
FIG. 8 is an enlarged plan view showing a configuration example of servo patterns performed such overlap writing.
As shown in FIG. 8, a servo pattern 8 comprises servo information 82 and burst 83. Using the R/W magnetic head, first servo information 82a and bust 83a bare written to one-side portion of a center line 85 of a data track 84. Thereafter, the R/W magnetic head is moved a half track pitch in a direction perpendicular to the data track 84 (radial direction of the floppy disk) and second servo information 82b and burst 83b are written (overlap write) in the same position as the first written position to form a servo pattern 81 wider than the data track 84. Also in this case, the servo information 82 is written in such a manner that the center line (information center) of each information area coincides with the center line (track center) 85 of each data track 84. As to the burst 83, it is written in such a manner that the outer and inner edges of each information area are respectively in contact with the center lines 85 (track centers) of adjacent data tracks 84.
According to the known servo pattern forming method for a floppy disk described above, in twice writing (overlap write) the servo pattern 81, especially burst 83, the written position of the first burst 83a and that of the second burst 83b may be shifted from each other in the track length direction, for example, due to slight unevenness in rotation of a spindle motor for rotating the floppy disk or due to external oscillations. Upon occurrence of such a positional shift, burst A (83A) located on one side of the center line 85 of the data track 84 and burst B (83B) located on the other side are not always equal to each other with respect to the amount of information, thus giving rise to the problem that it is no longer possible to accurately make a tracking correction using the burst A(83A) and burst B(83B).